This invention relates to a testable substrate or wafer and a testing method which enable efficient fabrication of an optical component mounting substrate on which an optical fiber and optical components (e.g., a light emitter and a light detector) to be optically coupled to each other while enabling an efficient testing of the optical components mounted on the optical component mounting substrate.
In recent years, toward the spread of communication systems of optical subscriber type, attention has been drawn to a passive alignment technique using a monocrystalline silicon substrate as a mounting substrate (this substrate is called silicon platform) in order to reduce an assembling cost of an optical module.
According to this technique, an optical module can be assembled without alignment only by mounting the optical fiber and the optical components such as a laser diode and a photodiode in a V-shaped groove or a conductor pattern formed on the same silicon substrate.
Such optical component mounting substrates are fabricated at once with V-shaped grooves for mounting the optical fibers and a plurality of conductor patterns for mounting the optical components arrayed on the same wafer, and are divided or split into individual substrates at a final process. FIGS. 16A and 16B shows an optical component mounting substrate J formed into a chip by dividing.
Fabrication of a multitude of optical component mounting substrates from one wafer is very advantageous in terms of production costs and is desirable in terms of cost reduction of the optical module. Further, the use of silicon wafers has an advantage of significant cost reduction at the time of mass-production since the mass-production technique of semiconductor devices can be employed.
However, even if the mounting substrates are fabricated by the wafer, it is extremely cumbersome and is considered to cause a cost increase to mount the optical components one by one on the mounting substrates in the form of a chip and to test the respective devices.
Accordingly, it is highly desirable to, similar to a so-called burn-in which has been conventionally employed in the semiconductor field, enable a detection of initial defects in a mounting process including defects of a plurality of optical components themselves after the optical components are mounted at once while employing a visual alignment technique, a solder self-alignment technique or like technique for mounting a multitude of optical components while observing mounting markers on a wafer.
In order to realize the above method, at least following problems have to be overcome.
1) In order to check initial deterioration of a light emitter and a light detector for monitoring a light from the light emitter which are provided on each substrate 50 in the form of a chip as shown in FIGS. 16A and 16B, not only electrical characteristics of these optical components, but also light emitting characteristics and light detecting characteristics thereof need to be measured. However, it is difficult to conduct these measurements with the conventional optical component mounting substrate J since no sufficient space can be provided for an optical detector for testing the light emitter and a light source for testing the light detector. In FIGS. 16A and 16B, indicated at 53, 54 are driving conductive lines for the light emitter, 15, 16 driving conductive lines for the light detector, 17 a V-shaped groove in which an optical fiber is laid, 18a a solder pattern on which the light emitter is mounted, and 16a a solder pattern on which the light detector is mounted.
2) If an attempt is made to electrically connect all electrodes similar to a wafer burn-in device used in the semiconductor field, not only many contact terminals, but also a highly expensive contactor for simultaneously connect the many contact terminals are necessary. Particularly, since the optical components are mounted in a hybrid manner, it is even more difficult to establish the above contacts without damaging them.
3) Although it may be considered to provide a wiring to conduct probing at an end of the wafer in order to avoid the problem 2), the wiring becomes complicated due to its intersections.
It is an object of the present invention to provide a testable substrate and a testing method which are free from the problems residing in the prior art.
It is another object of the present invention to provide a testable substrate and a testing method which enable a burn-in to be easily and readily performed to a wafer on which optical components are mounted all at once and also enable the optical components to be quickly tested.
According to an aspect of the invention, a testable substrate comprises a base member having a plurality of optical component mounting areas in which light emitters and light detectors for detecting lights emitted from the light emitters are to be mounted; a first insulating layer formed on the base member; a second insulating layer formed on the first insulating layer; two kinds of conductive lines connectable with opposite electrode terminals of light emitters mounted in the respective optical component mounting areas; and two kinds of conductive lines connectable with opposite electrode terminals of light detectors mounted in the respective optical component mounting areas, wherein at least one of the two kinds of conductive lines connectable with light emitters and at least one of the two kinds of conductive lines connectable with light detectors are laid on different ones of the first and second insulating layers.
According to another aspect of the invention, a testing method comprises the steps of preparing a substrate having a plurality of optical component mounting areas; mounting in the respective optical component mounting areas light emitters and light detectors for detecting light emitted from the light emitters; heating the substrate mounted with the light emitters and the light detectors to a predetermined temperature; and driving the light emitters and the light detectors with the substrate having the predetermined temperature to measure the amount of light emitted from each light emitter by the corresponding light detector.
With the above construction and method, the light emitters and the light detectors can be tested in their mounted states by mounting them in the respective optical component mounting areas, driving them via the respective conductive lines with the substrate heated at the predetermined temperature, and measuring the amounts of lights emitted from the respective light emitters by means of the corresponding light detectors. More specifically, the amount of light measured by the light detectors do not reach a specified value if there are defects in the light emitters and the light detectors themselves, errors made during an operation of mounting them, breakage of the conductive lines, and the like. A specified amount of light cannot be detected, either, if there is a displacement between the corresponding light emitters and light detectors during the mounting operation. Therefore, any defect in an optical module, e.g., defects in light emitters and light detectors, can be securely and quickly detected in optical component mounted states.